Axonal transport underlies neuronal growth, maintenance and regeneration. Movement of membrane- bounded organelles by fast axonal transport (FAT) is required for functions that include synaptic transmission, action potentials and neurotrophin supply. Study of molecular mechanisms for FAT provides insight into neuronal functions and pathology. Direct connections can be made between disruption of FAT and pathogenesisfor various neuropathological conditions, including Alzheimer's and Huntington's disease, and other dying back neuropathies. Studies of FAT in isolated axoplasm from squid led to our discovery of kinesins and now have identified specific regulatory pathways for transport in neurons. Proposed experiments extend our current studies on molecular mechanisms of FAT in three areas. First, we propose to define specific functional domains on kinesin-1 heavy and light chain isoforms important for regulation of transport and targeting of different cargos. Proposed studies combine methods from biochemistry, cell biology, immunochemistry, and molecular biology to delineate functional architecture of kinesin isoforms. Experiments under this aim will determine the physiological significance of posttranslational modifications on specific kinesin heavy and light chains. Second, pathways for regulation of kinesin-based motility in neurons will be mapped. Multiple signaling pathways that affect fast axonal transport have been identified. Proposed experiments will identify spatial and temporal patterns of kinesin-1 regulation in neurons, with a goal of identifying pathways important for delivery of cargos to specific neuronal domains. Finally, kinesins are implicated in the pathogenesis of polyglutamine expansion diseases. We propose to evaluate the role of kinesins in pathogenesis of Huntington's and other polyQ expansion diseases. Kinases activated by pathogenic polyQ proteins compromise kinesin-mediated motility in affected neurons. Planned experiments will define relevant pathways and their activation by pathogenic polyQ proteins. Proposedstudies will illuminate role for kinesin-1 in both normal neuronal function and neuropathology.